Range Finding

Replica Watkin Position Finder

Rinella Battery Malta

Horizontal Receiver Half Moon Battery Pendennis Castle

Horizontal Receiver 1914

Coast Defence Range Finding

To range the guns and give a bearing of targets for individual gun batteries range finding equipment was needed. In the Victorian period, as advances were made in the science of range finding and sighting guns, so coast batteries were fitted and updated with the latest range finders, position finders and fire control apparatus.

By the 1880s coast defence batteries were fitted with two types of range finder, the horizontal and the depression. These were invented and developed by Major, later Colonel, H.S.S. Watkin R.A. and the horizontal range finders were sometimes referred to as Watkin Position Finders.

The position finder was a highly complicated machine which transmitted to the gun mounting, by means of electrically operated dials, the correct gun range and training for engaging a hostile vessel. The position finder required a transmitting cell and a receiving cell with an instrument in each. The receiving instrument and its transmitting telescope form the base of the triangle to the target, this distance being known it is a simple matter to calculate the range of the target. Measurements from the transmitting instrument and receiving instrument were combined in the receiving cell. A range and bearing was then communicated to the gun battery via wires where it was displayed on the gun dials.

The depression range finder was at a known height above the water-line and by sighting a telescope on the target, the distance to the target could be calculated using the height of the range finder as the base of the triangle and the angle of depression. Depression Range Finders, mounted on pedestals within a battery, could give range and bearing of a target and provided less accurate but useful data for the gun batteries to range their guns should data not be available from the more accurate position finders due to weather conditions or damage. The Fire Commander also had a Depression Range Finder so that he could observe and correct fire.

Depression Range Finder Mark II

Depression Horizontal Receiver

Mark II Horizontal transmitter

Position Finder G

Watkin Position Finder

Watking Range Dial

Position Finder D Mark II

Position Finder D

Position Finder A Mark II

Specially adapted range finders were produced for Submarine Mining installations. These allowed the mines to be detonated from the position finding cell using electrical contacts on the table.

Diagram of a P.F. Cell for a Submarine mining Installation

Position Finding table

Position Finder Submarine Mining, Long Range Long Range Mark III

Position Finder Submarine Mining, Long Range Special

Depression Range Finders were mounted on a single pillar, sometime enclosed and sometimes in the open. Position Finders were mounted in position finding cells with the table supported on three concrete pillars.

Pedestal for Depression Range Finder

Position Finding Cells at Fort Gilkicker, Gosport

In 1886 the Assistant Director of Artillery and Stores stated that:

The Depression Position Finder.
The observing stations in which the instruments are placed should be situated well clear of the work if possible to the right or left and never immediately above it. They should be so designed and placed as to be concealed form the enemy and out of the probable line of his fire. Two sets of observing stations should be provided in order that one set should be available should the view from the other set be impeded by smoke. As the instrument now provided now requires no chart table the expense of these stations will be very trifling and therefore there should be no difficulty in increasing their number as proposed. The guns in the work should be divided into groups, the number in each and their distribution to depend on the contour and structure of the battery. Bearing in mind that the guns in a group will all be laid with this system with their axes parallel, the outside guns of any group should not be further apart than 100 feet horizontally. Each group requires a Position Finder and dial, the latter to be placed in a convenient position in the centre of the group. The instruments will be connected will be connected with their dials by means of a five core armoured cable efficiently protected from interruption by either the enemy's fire or other causes. The instruments require only four wires but the fifth will be available for a firing wire or in the case of interruption for any of the others.
The Depression Position finder will appear to be applicable to the following stations :- Portsmouth, Needles passage, Dover Portland, Malta, Gibraltar. Instruments
Plymouth 30
Portsmouth 8
Dover 6
Gibraltar 20
Malta 30
Portland Breakwater 12
Grand Total £50 per instrument plus costs £16,305

It was proposed to add Cork, Forts Camden and Carlisle, Aden and Bermuda to the lists of stations
to which Depression Position finders should be supplied.
5 & Cork
5 & Aden
8 & Bermuda

Electric Position Finder
The instrument now proposed by Major Watkin will allow of the same pattern range table as that for the Depression Position Finder now being used in the battery and also of the observing stations being wholly outside the fort as in the case of last named instrument, one of these observing stations will however must be of suitable dimensions for holding a chart or chart table. These instruments are only intended for works having less command of 60ft. above mean tide level. the arrangement for grouping the guns and for communication between them and the guns will be the same as for those of the depression position finder. Three observing stations will be required. two of these should be clear of the fort right or left and the third at such a distance as to give and effective working base. The following stations shall be supplied with electric position finders,
Portsmouth Spithead Forts 9 @ £60
Sheerness 4 @ £60
Landguard Fort 3 @ £60

D.R.F. Pedestal Fort Gilkicker

D.R.F. Pedestal No.2 Battery Stokes Bay

D.R.F. Pedestal Pendennis Castle

D.R.F. Pedestal Whitesand Bay Battery Plymouth

Position finding cell Staddon Heights Plymouth

Position finding cell Staddon Heights Plymouth

Receiving cell for Horizontal Position Finder at Fort Gilkicker, Gosport